1. Field of the Invention
The present invention relates to a process for producing a rocker arm for an internal combustion engine.
2. Description of the Prior Art
In general, in producing such a rocker arm, the following steps have been conventionally used: a step of fabricating a rocker arm blank formed of carburized steel, which has apertures adapted to be converted to shaft insertion holes provided therein; a step of subjecting the periphery of the apertures to a reaming operation to properly size and shape the shaft insertion holes; after such reaming, a step of subjecting the rocker arm blank to a carburization hardening treatment in order to increase the wear resistance, or the like, of an inner peripheral surface of each of the shaft insertion holes; a step of subjecting the rocker arm blank to a barreling in order to remove oxides from the surface of the rocker arm blank; and a step of subjecting the shaft insertion holes to a honing in order to remove such thermal strain as may have been introduced due to the carburization hardening treatment.
The reason why the shaft insertion holes are formed by reaming prior to the carburization hardening treatment as described above, is that the reaming can not be performed after the carburization hardening treatment, because the hardness of the inner wall of the shaft insertion holes is increased by the carburizing treatment.
With the prior art process, however, two machinings i.e., reaming and honing, are required for each shaft insertion hole, resulting in an increased number of steps needed to produce each rocker arm. In addition there is another problem. Each blank must be separately honed, resulting in a lower efficiency of production of the rocker arm. Thus, an increase in the cost of manufacturing the rocker arm cannot be avoided.